In this recipe, we are going to create the second of our two LVM abstraction layers. While the first layer provides an elastic base for DRBD, this one will provide most of the LVM functionality that we will actually use on a regular basis.
Tasks such as creating filesystem snapshots or reorganizing data are within the domain of the second layer. This is because we create the filesystem on top of this second LVM definition. We can mount or otherwise manipulate a snapshot like any other filesystem. If we tried to create a snapshot with the first LVM layer, we would still have a snapshot, but it would be of an unreadable DRBD binary blob.
With that in mind, let's add the LVM layer necessary for filesystem manipulation.